Liquid condition sensing apparatus

Abstract

Capacitive liquid condition sensing apparatus includes a pair of a 1 - 1 electrode and a 1 - 2 electrode arranged to form a first capacitance; a pair of a 2 - 1 electrode and a 2 - 2 electrode arranged to form a second capacitance; a circuit board formed with a sensing circuit to sense the liquid condition such as a liquid level in accordance with the first and second capacitances; and 1 - 1, 1 - 2, 2 - 1 and 2 - 2 conductive paths connecting the 1 - 1, 1 - 2, 2 - 1 and 2 - 2 electrodes, respectively, to the sensing circuit, and including 1 - 1, 1 - 2, 2 - 1 and 2 - 2 conductive segments, respectively. The 1 - 1, 1 - 2, 2 - 1 and 2 - 2 conductive segments are arranged in a row, and extend side by side. The 1 - 1, 1 - 2, 2 - 1 and 2 - 2 conductive segments are arranged so that a first parasitic capacitance formed between the 1 - 1 conductive segment and the 1 - 2 conductive segment is equal to a second parasitic capacitance formed between the 2 - 1 conductive segment and the 2 - 2 conductive segment.

1. A capacitive liquid condition sensing apparatus to be submerged at least partly in a liquid, for sensing a liquid condition of the liquid, the liquid condition sensing apparatus comprising:
 a first electrode pair of a  1 - 1  electrode and a  1 - 2  electrode arranged to form a first capacitance varying in accordance with a condition of the liquid; 
 a second electrode pair of a  2 - 1  electrode and a  2 - 2  electrode arranged to form a second capacitance varying in accordance with another condition of the liquid; 
 a circuit board formed with a sensing circuit to monitor the first and second capacitances and to sense the liquid condition in accordance with the first and second capacitances; 
 a  1 - 1  conductive path connecting the  1 - 1  electrode to the sensing circuit and including a  1 - 1  conductive segment; 
 a  1 - 2  conductive path connecting the  1 - 2  electrode to the sensing circuit and including a  1 - 2  conductive segment; 
 a  2 - 1  conductive path connecting the  2 - 1  electrode to the sensing circuit and including a  2 - 1  conductive segment; and 
 a  2 - 2  conductive path connecting the  2 - 2  electrode to the sensing circuit and including a  2 - 2  conductive segment; 
 wherein the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment are arranged in a row, and extend side by side; and 
 wherein the  2 - 1  conductive segment extends between the  1 - 1  conductive segment and the  1 - 2  conductive segment, and the  1 - 2  conductive segment extends between the  2 - 1  conductive segment and the  2 - 2  conductive segment. 
 
   
   
     2. The liquid condition sensing apparatus as claim in  claim 1 , wherein the sensing circuit comprises:
 a first grounding section to ground the  1 - 1  conductive path and the  1 - 2  conductive path; 
 a second grounding section to ground the  2 - 1  conductive path and the  2 - 2  conductive path; and 
 a capacitance measuring section to measure the first capacitance in a first measuring state in which at least one of the  1 - 1  conductive path and  1 - 2  conductive path is not grounded, and the  2 - 1  conductive path and the  2 - 2  conductive path are both grounded by the second grounding section; and to measure the second capacitance in a second measuring state in which at least one of the  2 - 1  conductive path and  2 - 2  conductive path is not grounded, and the  1 - 1  conductive path and the  1 - 2  conductive path are both grounded by the first grounding section. 
 
   
   
     3. A capacitive liquid condition sensing apparatus to be submerged at least partly in a liquid, for sensing a liquid condition, the liquid condition sensing apparatus comprising:
 a first electrode pair of a  1 - 1  electrode and a  1 - 2  electrode arranged to form a first capacitance varying in accordance with a condition of the liquid; 
 a second electrode pair of a  2 - 1  electrode and a  2 - 2  electrode arranged to form a second capacitance varying in accordance with a condition of the liquid; 
 a circuit board formed with a sensing circuit to monitor the first and second capacitances and to sense the liquid condition in accordance with the first and second capacitances; 
 a  1 - 1  conductive path connecting the  1 - 1  electrode to the sensing circuit and including a  1 - 1  conductive segment; 
 a  1 - 2  conductive path connecting the  1 - 2  electrode to the sensing circuit and including a  1 - 2  conductive segment; 
 a  2 - 1  conductive path connecting the  2 - 1  electrode to the sensing circuit and including a  2 - 1  conductive segment; and 
 a  2 - 2  conductive path connecting the  2 - 2  electrode to the sensing circuit and including a  2 - 2  conductive segment; 
 the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment being arranged in a row, and extending side by side; and 
 the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment being arranged so that a first parasitic capacitance formed between the  1 - 1  conductive segment and the  1 - 2  conductive segment is equal to a second parasitic capacitance formed between the  2 - 1  conductive segment and the  2 - 2  conductive segment. 
 
   
   
     4. The liquid condition sensing apparatus as claimed in  claim 3 , wherein the  1 - 1  conductive path further includes a  1 - 1  terminal connected by soldering with the  1 - 1  conductive segment, and a  1 - 1  connecting line connecting the  1 - 1  electrode to the  1 - 1  terminal;
 the  1 - 2  conductive path further includes a  1 - 2  terminal connected by soldering with the  1 - 2  conductive segment, and a  1 - 2  connecting line connecting the  1 - 2  electrode to the  1 - 2  terminal; 
 the  2 - 1  conductive path further includes a  2 - 1  terminal connected by soldering with the  2 - 1  conductive segment, and a  2 - 1  connecting line connecting the  2 - 1  electrode to the  2 - 1  terminal; 
 the  2 - 2  conductive path further includes a  2 - 2  terminal connected by soldering with the  2 - 2  conductive segment, and a  2 - 2  connecting line connecting the  2 - 2  electrode to the  2 - 2  terminal; and 
 the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  electrodes, the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  connecting lines and the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals are all formed integrally in an electrode board. 
 
   
   
     5. The liquid condition sensing apparatus as claimed in  claim 4 , wherein the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  electrodes, the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  connecting lines and the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals are all formed on a single layer in the electrode board. 
   
   
     6. The liquid condition sensing apparatus as claimed in  claim 5 , wherein the  2 - 1  connecting line includes a roundabout portion detouring the  1 - 1  terminal, and extending through a region which is so located that the  1 - 1  terminal is located between the first electrode pair and the region. 
   
   
     7. The liquid condition sensing apparatus as claimed in  claim 6 , wherein the  1 - 1  connecting line includes a longitudinally extending portion extending, in a longitudinal direction of the electrode board, to connect the  1 - 1  electrode to the  1 - 1  terminal, and the  2 - 1  connecting line includes a longitudinally extending portion extending along the longitudinally extending portion of the  1 - 1  connecting line, and the roundabout portion extending, in a lateral direction of the electrode board and connecting the longitudinally extending portion of the  2 - 1  connecting line with the  2 - 1  terminal, the  1 - 1  terminal is located, in the longitudinal direction, between the longitudinally extending portion of the  1 - 1  connecting line and the roundabout portion of the  2 - 1  connecting line, and, in the lateral direction, between the  2 - 1  terminal and the longitudinally extending portion of the  2 - 1  connecting line. 
   
   
     8. The capacitive liquid condition sensing apparatus as claimed in  claim 7 , wherein the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals are arranged in a row in the lateral direction of the electrode board, and the  2 - 1  terminal is located, in the lateral direction, between the  1 - 1  and  1 - 2  terminals. 
   
   
     9. The liquid condition sensing apparatus as claimed in  claim 4 , wherein the electrode board is a flexible board which comprises:
 a vertical zone in which the  2 - 1  and  2 - 2  electrodes are formed; 
 a horizontal zone in which the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals are formed; and 
 a bent zone bent between the vertical zone and the horizontal zone; and 
 the circuit board confronts the horizontal zone of the flexible board. 
 
   
   
     10. The liquid condition sensing apparatus as claimed in  claim 4 , wherein each of the conductive segments extends from a first end portion inserted into a through hole formed in a corresponding one of the terminals in the electrode board and a second end portion inserted into a corresponding one of through holes formed in the circuit board. 
   
   
     11. The liquid condition sensing apparatus as claimed in  claim 3 , wherein the  2 - 1  electrode and the  2 - 2  electrode of the second electrode pair extend side by side from respective lower portions adapted to be submerged in the liquid, to respective upper portions adapted to project above the surface of the fluid, and wherein the liquid condition sensing apparatus is a capacitive liquid level sensing apparatus for sensing a liquid level as the liquid condition, from the first capacitance between the  1 - 1  electrode and the  1 - 2  electrode of the first electrode pair and the second capacitance between the  2 - 1  electrode and the  2 - 2  electrode of the second electrode pair. 
   
   
     12. The liquid condition sensing apparatus as claimed in  claim 11 , wherein the first electrode pair is a reference electrode pair which is formed at a lower position to be submerged invariably in the liquid and which includes the  1 - 1  electrode that is a first reference electrode and the  1 - 2  electrode that is a second reference electrode arranged to form the first capacitance that is a reference capacitance invariable with the liquid level, and the second electrode pair is a measuring electrode pair which is formed at an upper lo position above the lower position and which includes the  2 - 1  electrode that is a first measuring electrode and the  2 - 2  electrode that is a second measuring electrode, arranged to form the second capacitance that is a measuring capacitance variable with the liquid level, and wherein the sensing circuit is configured to determine a ratio between the first capacitance and the second capacitance. 
   
   
     13. The capacitive liquid condition sensing apparatus as claimed in  claim 3 , wherein the  2 - 1  conductive segment extends between the  1 - 1  conductive segment and the  1 - 2  conductive segment, and the  1 - 2  conductive segment extends between the  2 - 1  conductive segment and the  2 - 2  conductive segment. 
   
   
     14. The capacitive liquid condition sensing apparatus as claimed in  claim 13 , wherein the sensing circuit of the circuit board comprises:
 a first grounding section to ground the  1 - 1  conductive path and the  1 - 2  conductive path; 
 a second grounding section to ground the  2 - 1  conductive path and the  2 - 2  conductive path; and 
 a capacitance measuring section to measure the first capacitance in a first measuring state in which at least one of the  1 - 1  conductive path and  1 - 2  conductive path is not grounded, and the  2 - 1  conductive path and the  2 - 2  conductive path are both grounded by the second grounding section; and to measure the second capacitance in a second measuring state in which at least one of the  2 - 1  conductive path and  2 - 2  conductive path is not grounded, and the  1 - 1  conductive path and the  1 - 2  conductive path are both grounded by the first grounding section. 
 
   
   
     15. The liquid condition sensing apparatus as claimed in  claim 3 , the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment are, respectively, a  1 - 1  lead pin, a  1 - 2  lead pin, a  2 - 1  lead pin and a  2 - 2  lead pin, and each of the lead pins is surrounded by a dielectric higher in dielectric constant than air. 
   
   
     16. The liquid condition sensing apparatus as claimed in  claim 15 , wherein the liquid condition sensing apparatus further comprises an electrode board integrally formed with the  1 - 1  electrode and the  1 - 2  electrode of the first electrode pair, and the  2 - 1  electrode and the  2 - 2  electrode of the second electrode pair. 
   
   
     17. The capacitive liquid condition sensing apparatus as claimed in  claim 3 , wherein the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment are arranged so that a first distance between the  1 - 1  conductive segment and the  1 - 2  conductive segment is equal to a second distance between the  2 - 1  conductive segment and the  2 - 2  conductive segment, and wherein the  2 - 1  electrode and the  2 - 2  electrode of the second electrode pair are adapted to extend vertically. 
   
   
     18. The liquid condition sensing apparatus as claimed in  claim 17 , wherein the  2 - 1  conductive segment extends between the  1 - 1  conductive segment and the  1 - 2  conductive segment, and the  1 - 2  conductive segment extends between the  2 - 1  conductive segment and the  2 - 2  conductive segment. 
   
   
     19. The liquid condition sensing apparatus as claimed in  claim 3 , wherein the liquid condition sensing apparatus comprises an electrode board extending longitudinally from a first end to a second end, and including the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  electrodes, and  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals connecting the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  electrodes, respectively, to the sensing circuit, the second electrode pair is formed in the electrode board between the second end and the first electrode pair, and the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals are formed in the electrode board between the first end and the first electrode pair, and wherein the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment are connected, respectively, with the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals. 
   
   
     20. The liquid condition sensing apparatus as claimed in  claim 19 , wherein the electrode board includes a vertical zone in which the second electrode pair is formed, and a horizontal zone in which the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  terminals are formed. 
   
   
     21. The capacitive liquid condition sensing apparatus as claimed in  claim 3 , wherein the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment are parallel to one another; and wherein the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment are identical in shape and size with one another and wherein the  1 - 1  electrode and the  1 - 2  electrode of the first electrode pair are formed in a first region and elongated in a lateral direction whereas the  2 - 1  electrode and the  2 - 2  electrode of the second electrode pair extend, from the first region, in a longitudinal direction perpendicular to the lateral direction. 
   
   
     22. The liquid condition sensing apparatus as claimed in  claim 3 , wherein the liquid condition sensing apparatus further comprises an electrode board extending longitudinally from a first end to a second end, and including a measuring zone in which the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  electrodes are formed, and a connection zone located between the measuring zone and the first end of the electrode board, and the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment extend from the connecting zone away from the measuring zone. 
   
   
     23. The liquid condition sensing apparatus as claimed in  claim 3 , wherein the  1 - 1 ,  1 - 2 ,  2 - 1  and  2 - 2  electrodes are formed in a first region whereas the  1 - 1  conductive segment, the  1 - 2  conductive segment, the  2 - 1  conductive segment and the  2 - 2  conductive segment are arranged in the row in a second region located on one side of the first region.